The Pirates received infielder/outfielder Tucupita Marcano, right-hander Michell Miliano and outfielder Jack Suwinski in exchange for Frazier. According to the teams, Pittsburgh also sent $1.4 million to the Padres in the deal.
"Good job by our scouting department, our development department and obviously Adam to turn himself into a really good Major League player," Pirates general manager Ben Cherington told reporters. "He did a really good job for the Pirates. We wish him the very best in San Diego."
Entering Monday, Frazier ranked first in MLB with 125 hits. He also had a .324 batting average with four home runs and 32 RBIs over 98 games this season for the Pirates.
The 29-year-old Frazier, who isn't a free agent until after the 2022 season, earned All-Star honors for the first time in his six-year career this summer. The 2020 Gold Glove finalist was the Pirates' second-longest-tenured player -- behind right fielder Gregory Polanco -- before the trade.
Marcano, 21, has a .272 batting average with six home runs and 26 RBIs for Triple-A El Paso. He has played shortstop, second base and in the outfield this season.
The 22-year-old Suwinski has bashed 15 home runs for Double-A San Antonio this season.
Miliano, 21, has a 2-2 record and 3.60 ERA with two saves in Class A this year.